The present invention relates to an image generation system, a program, an information storage medium and an image generation method.
In the prior art, there is known an image generation system (or game system) for generating an image visible from a virtual camera (or a given viewpoint) in an object space which is a virtual three-dimensional space. It is highly popular as a method by which a so-called virtual reality can be experienced. If an image generation system which can play a role playing game (RPG) is considered herein as an example, a player can enjoy the game by controlling a character (or object) who is its own duplicate such that it moves on a map in the object space to fight against an enemy character, to dialogue any other character or to visit various towns.
Such an image generation system may be required to display a game scene covered with fog, mist, smoke, dust or the like which will generically be referred to “fog” later. To improve the player's feel of virtual reality, it is desired that the nonuniformity of the fog can realistically be represented.
One technique for representing such nonuniformity in the fog may be to use a billboard of translucent polygon. In this technique, a plurality of translucent polygons on each of which a nonuniformity pattern in the fog is mapped are provided. These translucent polygons are arranged directly facing a virtual camera in the direction of depth.
However, this technique generates an unnatural image since intersection lines between the translucent polygons used to represent the fog and the other polygons are visible.